The precise location of the replication terminus on the chromosome of Escherichia coli is being determined by various procedures. DNA obtained from cells terminating the replication cycle after various treatments is being hybridized with DNA obtained from F' episomes or from defective transducing phage that contains DNA from the region near the terminus. Similar procedures are being used to determine if the usual bidirectional replication pattern of the E. coli chromosome is ever altered, and if different regions can act as the origin or terminus of replication. Of particular interest are cells exhibiting integrative suppression of different temperature sensitive DNA synthesis mutations. Genetic crosses are also being conducted to determine if the location of the terminus can be determined by this procedure. The crosses are being performed in conditions in which the state of the terminus DNA might produce a discontinuity in the normal linkage of genes. The association between the replication terminus and the cell membrane is being examined at various stages of the cell cycle to determine if such an association is involved in the segregation of daughter chromosomes and the control of cell division.